Nitrogen substituted carbon and silicon clathrates

ABSTRACT

Compositions comprising Type I clathrates of silicon (Si 46 ) or carbon (C 46 ) wherein the framework of the cage structure includes nitrogen and carbon or nitrogen and silicon or nitrogen-silicon-carbon atom type composition, with or without guest atoms in their respective cage structures. The clathrate structures are particularly useful for energy storage applications such as battery electrodes.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. application Ser. No.14/022,822, filed Sep. 10, 2013, the teachings of which are incorporatedherein by reference.

FIELD OF THE INVENTION

The present disclosure relates to the compositions, structures andsynthesis method of clathrate compounds wherein the framework of thecage structure includes nitrogen and carbon atoms or nitrogen andsilicon atoms or a nitrogen-carbon-silicon atom composition, with andwithout guest atoms in their respective cage structures. Theseclathrates are suitable for use as thermoelectric materials, electronicmaterials, energy storage and relatively high modulus materials.

BACKGROUND

U.S. application Ser. No. 12/842,224 discloses, among other things, anelectrode and methods for forming such electrode for a battery whereinthe electrode comprises silicon clathrate. The silicon clathrate mayinclude silicon clathrate Si₄₆ containing an arrangement of 20-atom and24-atom cages fused together through 5 atom pentagonal rings and/orsilicon clathrate Si₃₄ containing an arrangement of 20-atom and 28-atomcages fused together through 5 atom pentagonal rings.

U.S. application Ser. No. 13/109,704 discloses, among other things,clathrate (Type I) allotropes of silicon, germanium and tin that may beused for an electrode in lithium-ion batteries.

U.S. application Ser. No. 13/452,403 discloses, among other things,alloy cage structures of silicon, germanium and/or tin for use as anelectrode in rechargeable batteries.

U.S. application Ser. No. 13/924,949 discloses, among other things, thecomposition and synthesis of clathrate compounds with a silicon andcarbon framework.

SUMMARY

A composition comprising a Type I clathrate of carbon having a C₄₆framework cage structure wherein the carbon atoms on said framework areat least partially substituted by nitrogen atoms, said compositionrepresented by the formula N_(y)C_(46-y) with 1≦y≦45. The compositionmay include guest atoms as represented by the formula A_(x)N_(y)C_(46-y)where, A=H, Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Eu, Cl, Br,I, and any metal or metalloid element, with 1≦y≦45 and x is the numberof guest atoms within said cage structure.

A composition comprising a Type I clathrate of silicon having a Si₄₆framework cage structure wherein the silicon atoms on said framework areat least partially substituted by nitrogen atoms, said compositionrepresented by the formula N_(y)Si_(46-y) with 1≦y≦45. The compositionmay include guest atoms as represented by the formulaA_(x)N_(y)Si_(46-y) where, A=H, Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr,Ba, Ra, Eu, Cl, Br, I, and any metal or metalloid element, with 1≦y≦45and x is the number of guest atoms within said cage structure.

A composition comprising a Type I clathrate of silicon having a Si₄₆framework cage structure wherein the silicon atoms on said framework areat least partially substituted by nitrogen and carbon, said compositionrepresented by the formula N_(y)C_(z)Si_(46-y-z) with 1≦y≦44 and1≦z≦45−y. The composition may include guest atoms represented by theformula A_(x)N_(y)C_(z)Si_(46-y-z) where, A=H, Li, Na, K, R b, Cs, Fr,Be, Mg, Ca, Sr, Ba, Ra, Eu, Cl, Br, I, and any metal or metalloidelement, with 1≦y≦45 and 1≦z≦45−y and x is the number of guest atomswithin said cage structure.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description below may be better understood with referenceto the accompanying figures which are provided for illustrative purposesand are not to be considered as limiting any aspect of the invention.

FIG. 1 illustrates Si₂₀ and Si₂₄ cages as the building unit of therepresentative Type I Si₄₆ clathrate, without guest atoms.

FIG. 2 compares the energy of formation of A_(x)C_(y)Si_(46-y),A_(x)N_(y)C_(46-y) and A_(x)N_(y)Si_(46-y) against those of C₄₆ and Si₄₆clathrates as a function of lattice parameter showing nitrogensubstitution of the framework atoms on C₄₆ or Si₄₆ results in stablecarbon or silicon clathrate compounds.

FIG. 3 illustrates a Type I N_(y)C_(46-y) clathrate or anitrogen-silicon clathrate, N_(y)Si_(46-y), without guest atoms.

FIG. 4 illustrates a Type I guest-atom stabilized nitrogen-carbonclathrate (A_(x)N_(y)C_(46-y)) or nitrogen-silicon clathrate(A_(x)N_(y)Si_(46-y)) with x number of guest atoms A within the cage.

FIG. 5 illustrates the values of the energy of formation ofN_(y)Si_(46-y) are compared against those of C₄₆, Si₄₆ andLi_(x)N_(y)C_(46-y).

FIG. 6 illustrates the computed values of the energy of formation peratom for C₄₆, N_(y)C_(46-y), and Li_(x)N_(y)C_(46-y) are compared as afunction of the lattice parameter.

FIG. 7 illustrates powder x-ray diffraction patterns measured for theindicated compositions subsequent to arc-melting of powdered admixtureof Ba and g-C₃N_(4+x)H_(y).

DETAILED DESCRIPTION

Silicon clathrate Si₄₆ comprises crystalline Si with a regulararrangement of 20-atom and 24-atom cages fused together through 5 atompentagonal rings (Type I clathrate). It has a simple cubic structurewith a lattice parameter of 10.335 Å and 46 Si atoms per unit cell. FIG.1 illustrates the cage structure of the Si₄₆, which belongs to the Spacegroup Pm3n and Space Group Number 223. The crystal structure of thesilicon clathrate (Si₄₆) is different from the common form ofcrystalline Si (c-Si), which is diamond cubic with a lattice parameterof about 5.456 Å and belongs to the Space Group Fd3m, Number 227.

Another form of silicon clathrate is Si₃₄ (Type II clathrate) thatcomprises crystalline Si with a regular arrangement of 20 atoms and 28atom cages fused together through five-atom pentagonal rings. Type IISi₃₄ clathrate has a face-centered cubic (fcc) structure, with 34 Siatoms per fcc unit cell. The Si₃₄ clathrate has a lattice parameter of14.62 Å and belongs to the Space Group Fd3m, Number 227. Type II siliconclathrate is sometimes referred to as Si₁₃₆ since the compound containsfour fcc unit cells. A third form of silicon clathrate is a modificationof the Si₄₆ type formed by removing four atoms from the 24-atom cages.

Theoretical computations have shown that both Type I carbon clathrate(C₄₆) and Type II carbon clathrate (C₁₃₆ or C₃₄) may exist as metastablephases under high pressures. The cage structure of Type I carbonclathrate, C₄₆, is similar to that of Si₄₆ shown in FIG. 1. Insertion ofguest atoms such as Li, Na, or Ba into the cage structures has beenpredicted to be feasible under high pressures. However, the energy offormation for the Type I and Type II carbon clathrates are extremelyhigh and as presently known the syntheses of neither Type I nor Type IIcarbon clathrates have been reported.

FIG. 2 is a summary plot that depicts the energy of formation forcarbon-substituted and nitrogen-substituted clathrate compounds, whichinclude A_(x)C_(y)Si_(46-y), A_(x)N_(y)C_(46-y), andA_(x)N_(y)Si_(46-y), against those of C₄₆ and Si₄₆. Nitrogensubstitution was therefore identified to lower the energy of formationand produce stable carbon and silicon clathrates. These computations ledto the identification of three new classes of nitrogen-substituted TypeI clathrates based on the carbon or silicon framework: (1) N-substitutedcarbon clathrates (N_(y)C_(46-y)), (2) N-substituted silicon clathrates(N_(y)Si_(46-y)), and (3) N-substituted hybrid carbon silicon clathrates(N_(y)C_(z)Si_(46-y-z)).

Carbon-Nitrogen Clathrates

Computational studies on the Type I carbon and silicon clathrateallotropes indicated that the carbon atoms in the theoretical C₄₆framework can be partially substituted by nitrogen atoms to form ahybrid carbon-nitrogen clathrate, which can be represented byN_(y)C_(46-y). FIG. 3 shows a representation of the Type I N_(y)C_(46-y)clathrate or nitrogen-silicon clathrate, N_(ySi46-y), without guestatoms. Accordingly, guest atoms can be inserted into such cage structureto stabilize the clathrate by reducing the energy of formation to form,e.g., a class of nitrogen-substituted carbon clathrates, represented asA_(x)N_(y)C_(46-y), where A indicates the guest atom. FIG. 4 shows astructural representation of the Type I A_(x)N_(y)C_(46-y) clathratecompounds where x has a value of 0-200. That is, the value of x willdepend upon the size of guest atom introduced. The values of the energyof formation of N_(y)Si_(46-y) are compared against those of C₄₆, Si₄₆and Li_(x)N_(y)C_(46-y) in FIG. 5. For the compositions considered, theN_(y)Si_(46-y) compounds are stable compounds as their energy offormation values are negative.

Expanding upon the above, the N_(y)C_(46-y) clathrate contains ynitrogen atoms and 46−y carbon atoms with a regular arrangement of20-atom and 24-atom cages fused together through 5 atom pentagonal rings(Type I clathrate). It has a simple cubic structure with a latticeparameter in the range of 6.66 {acute over (Å)} to 6.86 {acute over (Å)}and a combined sum of 46 N and C atoms per unit cell. In addition,vacancies can be inserted into the N-substituted carbon framework andthe sum of N atoms, C atoms and vacancies is 46. The number of vacanciesmay range from zero to eight (8). Like Si₄₆, the crystal structure ofN_(y)C_(46-y) clathrate belongs to the Space group Pm3n, Number 223. Thenumber of N atoms on the nitrogen-carbon framework lies between 1 and 45(1≦y≦45).

In the case of guest atoms disposed in the carbon-nitrogen clathrates,as noted, the general formula is A_(x)N_(y)C_(46-y) where, A=H, Li, Na,K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Eu, Cl, Br, I, and any metal ormetalloid element capable of occupying the empty spaces inside the cagesof this Type I clathrate structure. Examples include, but are notlimited to, Ba_(x)N₁₈C₂₃, Ba_(x)N₁₈C₂₈, Ba_(x)N₁₈C₂₄, Ba_(x)N₂₃C₂₃,Li_(x)N₁₈C₂₃, Li_(x)N₁₈C₂₈, Li_(x)N₁₈C₂₄, Li_(x)N₂₃C₂₃, or similarpermutations of C and N with y being an integer, a fraction, or a numberplus a fractional part. In all cases, however, it is understood that Cand N constitute the clathrate crystallographic structure belonging tothe space group Pm3n and A_(x) represent guest atoms occupying the voidvolume of the clathrate cages. The number of guest atoms, x, that canoccupy inside the cage structure depends on the atomic size of A. Forrelatively large atoms such as Ba, the number of Ba atoms intercalatedwithin the cage structure is preferably eight or less (0≦x≦8). Forrelatively smaller atoms such as Li, the number of Li atoms, x,intercalated within the cage structures depends on the specific form andstoichiometric ratio of C and N, but in practical terms x is limited toa value defined by the onset of significant expansion of the latticeparameter, beyond which irreversible structural damage is likely tooccur in the bulk material.

Accordingly, in the clathrate structure defined by the equationA_(x)N_(y)C_(46-y) may be understood as one that, upon intercalcation ofguest atom A, the value of x is selected such that the cage structurewill preferably undergo a volume expansion of less than or equal to50.0%, or in the range of 0.1% to 50.0% in 0.1% increments. In relatedcontext, the clathrate structure is one that upon deintercalcation,preferably undergoes a volume change (contraction) of 50.0% or less, orin the range of 0.1% to 50.0% in 0.1% increments.

It can next be noted that the energy of formation for thecarbon-nitrogen and silicon-nitrogen clathrates with Li guest atoms werecomputed using the first-principles Car-Parrinello Molecular Dynamics(CPMD) code. The computed values of the energy of formation per atom forC₄₆, N_(y)C_(46-y), and Li_(x)N_(y)C_(46-y) are compared as a functionof the lattice parameter in FIG. 6, which compares the energy offormation for C₄₆ and N_(y)C_(46-y) without and with Li guest atoms.Nitrogen substitution lowers the energy of formation of N_(y)C_(46-y)compared to that for C₄₆. Li insertion reduces the energy of formationfurther to negative values, which indicates that Li_(x)N_(y)C_(46-y) arestable compounds.

More specifically, insertion of Li atoms into N-substituted carbonclathrates reduces the energy of formation but increases the latticeconstant of the unit cell. Type I, N-substituted carbon clathrates withLi guest atoms, represented by the formula Li_(x)N_(y)C_(46-y), has asimple cubic structure with a lattice parameter in the range of 6.66 Åto 9.32 Å. The N-substituted carbon framework has a combined sum of 46 Nand C atoms per unit cell and the number of Li guest atom ranges from 0to 48 (0<x<48) for the range of lattice parameter cited. In addition,vacancies can again be inserted into the N-substituted carbon frameworkand the sum of N atoms, C atoms, and vacancies remains 46. The crystalstructure of the Li_(x)N_(y)C_(46-y) clathrates belongs to the Spacegroup Pm3n, Number 223. The number of N atoms on the hybridnitrogen-carbon framework including the guest atoms again lies between 1and 45 (1≦y≦45).

Nitrogen-Silicon Clathrates

As alluded to above, the silicon atoms on the Si₄₆ framework can now bepartially substituted by nitrogen to form a nitrogen-silicon clathrate,represented by the formula N_(y)Si_(46-y). See again, FIG. 3. TheN_(y)Si_(46-y) clathrate can also be configured with guest atoms leadingto the formula A_(x)N_(y)Si_(46-y). More specifically, nitrogen-siliconframework that is represented by N_(y)Si_(46-y) comprises y nitrogenatoms and 46−y silicon atoms with a regular arrangement of 20-atom and24-atom cages fused together through 5 atom pentagonal rings (Type Iclathrate). It has a simple cubic structure with a lattice parameter inthe range of 9.0 Å to 10.23 Å and a combined sum of 46 N and Si atomsper unit cell. In addition, vacancies can be inserted into theN-substituted silicon framework and the sum of N atoms, Si atoms, andvacancies remains 46. The number of vacancies may range from zero toeight (8). The crystal structure of the N_(y)Si_(46-y) clathratesbelongs to the Space group Pm3n, Number 223. The number of N atoms onthe hybrid nitrogen-silicon framework lies between 1 and 45 (1≦y≦45).

As therefore noted, nitrogen-silicon clathrates stabilized by guestatoms are represented by the formula A_(x)N_(y)Si_(46-y), where A=H, Li,Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Eu, Cl, Br, I, and any metalor metalloid element capable of occupying the empty spaces inside thelarge cages of the Type I clathrate structure. Examples include, but arenot limited to, Ba_(x)N₁₈Si₂₃, Ba_(x)N₁₈Si₂₈, Ba_(x)N₁₈Si₂₄,Ba_(x)N₂₃Si₂₃, Li_(x)N₁₈Si₂₃, Li_(x)N₁₈Si₂₈, Li_(x)N₁₈Si₂₄,Li_(x)N₂₃Si₂₃, or similar permutations of N and Si with y being aninteger, a fraction, or a number plus a fractional part. In all cases,however, it is understood that N and Si constitute the clathratecrystallographic structure belonging to the space group Pm3n and A_(x)represent guest atoms occupying the void volume of the clathrate cages.The number of guest atoms, x, that can occupy inside the cage structuredepends on the atomic size of A and may range from zero to 200 or evenhigher, depending on the size of the guest atom. For relatively largeatoms such as Ba, the number of Ba atoms intercalated within the cagestructure is eight or less (0≦x≦8). For relatively small atoms such asLi, the number of Li atoms, x, intercalated within the cage structuresdepends on the specific form and stoichiometric ratio of N and Si, butin practical terms x is limited to a value defined by the onset ofsignificant expansion of the lattice parameter, beyond whichirreversible structural damage is likely to occur in the bulk material.

Accordingly, in the clathrate structure defined by the equationA_(x)N_(y)Si_(46-y) may be understood as one that, upon intercalcationof guest atom A, the value of x is selected such that the cage structurewill preferably undergo a volume expansion of less than or equal to50.0%, or in the range of 0.1% to 50.0% in 0.1% increments. In relatedcontext, the clathrate structure is one that upon deintercalcation,preferably undergoes a volume change (contraction) of 50.0% or less, orin the range of 0.1% to 50.0% in 0.1% increments.

More specifically, insertion of Li atoms into N-substitutedcarbon-silicon clathrates reduces the energy of formation but increasesthe lattice constant of the unit cell. Type I, N-substitutedcarbon-silicon clathrates with Li guest atoms, represented by theformula Li_(x)N_(y)C_(z)Si_(46-y-z), has a simple cubic structure with alattice parameter in the range of 6.4 Å to 10.4 Å. The N-substitutedsilicon framework has a combined sum of 46 N, C, and Si atoms per unitcell and the number of Li guest atom ranges from 0 to 48 (0<x<48) forthe range of lattice parameter cited. In addition, vacancies can beinserted into the N-substituted carbon-silicon framework and the sum ofN atoms, C atoms, Si atoms, and vacancies remains 46. The number ofvacancies may range from zero to eight (8). The crystal structure of theLi_(x)N_(y)C_(z)Si_(46-y-z) clathrate belongs to the Space group Pm3n,Number 223. The number of N atoms on the hybrid nitrogen-siliconframework can lie between 1 and 44 (1≦y≦44) and the number of C atoms onthe hybrid nitrogen-carbon-silicon framework can lie between 1 and 45−y(1≦z≦45−y), while the total number of C, N, Si, and vacancies, ifpresent, must be 46.

Nitrogen/Carbon/Silicon Clathrates

As alluded to above, the present disclosure also is directed at Type Initrogen-carbon-silicon clathrates with nitrogen, carbon and siliconatoms in the framework of the cage wherein the composition isrepresented by the formula N_(y)C_(z)Si_(46-y-z) with 1≦y≦44 and1≦z≦45−y.

In addition, the present disclosure also is directed atnitrogen-carbon-silicon clathrates stabilized by guest atoms representedby the formula A_(x)N_(y)C_(z)Si_(46-y-z), where A=H, Li, Na, K, Rb, Cs,Fr, Be, Mg, Ca, Sr, Ba, Ra, Eu, Cl, Br, I, and any metal or metalloidelement capable of occupying the empty spaces inside the large cages ofthe Type I clathrate structure. The value of x may be zero to 200 orgreater, depending upon the size of the guest atom.

Examples include, but are not limited to, Ba_(x)N₈C₁₀Si₂₃,Ba_(x)N₈C₁₀Si₂₈, Ba_(x)N₈C₁₀Si₂₄, Ba_(x)N₈C₁₄Si₂₄, Li_(x)N₈C₁₀Si₂₃,Li_(x)N₈C₁₀Si₂₈, Li_(x)N₈C₁₀Si₂₄, Li_(x)N₈C₁₄Si₂₄, or similarpermutations of N, C and Si with y being an integer, a fraction, or anumber plus a fractional part and with z being an integer, a fraction,or a number plus a fractional part. In all cases, however, it isunderstood that N, C and Si constitute the clathrate crystallographicstructure belonging to the space group Pm3n and A_(x) represent guestatoms occupying the void volume of the clathrate cages. The number ofguest atoms, x, that can occupy inside the cage structure depends on theatomic size of A. For relatively large atoms such as Ba, the number ofBa atoms intercalated within the cage structure is eight or less(0≦x≦8). For relatively small atoms such as Li, the number of Li atoms,x, intercalated within the cage structures depends on the specific formand stoichiometric ratio of N, C and Si. Accordingly, x is limited to avalue defined by the onset of significant expansion of the latticeparameter, beyond which irreversible structural damage is likely tooccur in the bulk material.

Accordingly, in the clathrate structure defined by the equationA_(x)N_(y)C_(z)Si_(46-y-z) may be understood as one that, uponintercalcation of guest atom A, the value of x is selected such that thecage structure will preferably undergo a volume expansion of less thanor equal to 50.0%, or in the range of 0.1% to 50.0% in 0.1% increments.In related context, the clathrate structure is one that upondeintercalcation, preferably undergoes a volume change (contraction) of50.0% or less, or in the range of 0.1% to 50.0% in 0.1% increments.

Methods of Preparation

In the present disclosure, by way of representative example, a cagestructure including guest atoms was prepared for the carbon-nitrogenclathrates noted above. Specifically, Ba₈C₁₈N₂₄ has been synthesized byarc-melting appropriate amounts of Ba and graphitic carbon nitride(g-C₃N_(4+x)H_(y)) as the starting materials. Admixtures of Ba andg-C₃N_(4+x)H_(y) (in the proportion of 20.6 g Ba, and 4.51 g ofg-C₃N_(4+x)H_(y) powders) was arc-melted to make about 25.11 g ofproduct, consisting of Ba₈C₁₈N₂₄ plus some amounts of unreacted startingmaterials.

Powder XRD data of the arc-melted product (i.e., not purified) ispresented in FIG. 7. Some of the reflection peaks in the XRD spectracorrespond to unreacted Ba and g-C₃N_(4+x)H_(y) starting materials,where the value of x ranges from 0 to 0.1 (0<x<0.1) and the value of yalso ranges from 0 to 0.1 (0<y<0.1). However, the remaining reflectionsin the XRD spectra do not belong to Ba and g-C₃N_(4+x)H_(y) and havebeen assigned to the clathrate structure of the present invention. Thetheoretically-computed reflections for Ba₈C₁₈N₂₄ were obtained by firstoptimizing the Type I clathrate structures using first principlesCar-Parrinello Molecular Dynamics (CPMD) computations to derive theequilibrium crystallographic parameters, followed by computing thecorresponding reflections in the XRD spectrum using the analysis andvisualization software called Diamond. The comparison indicates thatquantities of Type I clathrate compound are present in the arc-meltedBa₈C₁₈N₂₄ product. The crystal structure of this clathrate compound isclose to those of Ba₈N₁₈N₂₄ based on the characteristic reflections at2θ of 16.9°, 24.0°, 26.9°, 34.3°, 44.9° and 49.2° for thenitrogen-substituted carbon clathrate.

Applications

It is now useful to point out the various beneficial attributes andutility for the above disclosed compositions of Type I clathrates ofnitrogen-carbon, nitrogen-silicon, and nitrogen-carbon-silicon with orwithout guest atoms. In such compositions, the band structure and, inparticular, the electrochemical work function of the alloy clathratesmay be tuned by either altering the number of nitrogen atoms on thehybrid nitrogen-carbon, nitrogen-silicon, and nitrogen-carbon-siliconframework or by altering the guest atoms inserted into the cagestructure of clathrate system. These electronic characteristics makethis class of Type I clathrates suitable for applications asthermoelectric, electronic, energy storage, and high modulus materials.

A hybrid nitrogen, carbon, and Si framework can lead to delocalizationof the band structure, reduce the band gap, and increase the electronicconductivity of the clathrate compound. The presence of nitrogen atomson the clathrate framework can result in a smaller lattice constant andless empty space in the cage structure so that there is more electronicinteraction between the guest atom and the nitrogen substituted hybridSi and C atoms on the framework. These interactions can be tuned toenhance the Seebeck effects and electronic conductivity, alter the bandgap, and reduce the thermal conductivity by adjusting the number ofnitrogen atoms on the framework, the size, and the type of guest atomsinside the cage structure. For applications as energy storage materials,the band structure and, in particular, the electrochemical work functionof the anode and cathode for combinations of electrodes with uniqueclathrate-alloy compositions may be tuned to be compatible with the restof the battery system, including the absolute energies of the highestoccupied molecular orbital (HOMO) and the lowest unoccupied molecularorbital (LUMO) of the electrolyte. This tunability of the anode andcathode may be accomplished by adjusting the stoichiometric ratios ofN/A, C/A, Si/A, where A is the guest atom, or elemental form such that adesirable open-circuit potential is obtained in the charged state of thebattery within a thermodynamically-stable energy range of theelectrolyte. Thus, using appropriate ratios and/or elemental forms ofN/A, C/A and Si/A may yield a small work function necessary for theclathrate-alloy composition to function as an anode, whereas differentratios and/or elemental form of N/A, C/A and Si/A may be used to yield alarge work function necessary for the clathrate-alloy composition tofunction as a cathode. The battery couple (anode+cathode) that resultsis, therefore, based on a single class of material chemistry, thoughwith unique ratios and elemental forms of N/A, C/A and Si/A.

Accordingly, it can be appreciated that the Type 1 carbon-nitrogenclathrates, Type 1 nitrogen-silicon clathrates, or Type 1nitrogen-carbon-silicon clathrates herein, with or without guest atoms,may be configured such that they may be: (1) of particle form having thelargest linear dimension of 0.1 μm to 100.0 μm; (2) be of electrode formwherein the electrode comprises a metal substrate and the clathratealloy structure is present on the surface of the metal substrate; (3) beof any of the formulas noted herein: N_(y)C_(46-y), A_(x)N_(y)C_(46-y),N_(y)Si_(46-y), A_(x)N_(y)Si_(46-y), N_(y)C_(z)Si_(46-y-z), orA_(x)N_(y)C_(z)Si_(46-y-z), where A may be Li; (4) be of anode electrodeform in a Li battery; (5) be of cathode electrode form in a Li battery.A Li battery may be understood as a rechargeable battery in whichlithium ions move from a negative electrode to a positive electrodeduring discharge and when charging. During discharge lithium ions Li⁺carry current from the negative to the positive electrode through anon-acqueous electrolyte and separator diaphragm.

Finally, the bulk modulus of the various intermetallic clathratecompounds disclosed herein was also computed using the first-principlesapproach according to the expression given by:

$\frac{\Delta \; E}{V} = {\frac{9}{2}B\; \delta^{2}}$

where ΔE/V is the energy change per unit cell volume, B is the bulkmodulus, and δ is the normal strain in the three principal directions ofthe unit cell. A plot of ΔE/V versus δ was obtained for each unit cellof individual clathrate compounds and the data was fitted to the aboveequation. The regression coefficient was then used to obtain the bulkmodulus, B. A summary of the theoretical bulk modulus for variousintermetallic clathrate compounds is represented in Table 1 below whereexperimental values are indicated by an asterisk (*)

TABLE 1 Theoretical And Experimental Bulk Moduli Values CompoundStructure B, GPa C₄₆ Type I Clathrate 373.7 (Simple cubic) 409 363.7 371C₁₈N₂₄ Type I Clathrate 257.35 C₂₃N₂₃ Type I Clathrate 311.6 Li₈C₂₃N₂₃Type I Clathrate 245.18 Si₂₃C₂₃ Type I Clathrate 124.03 Si₆C₄₀ Type IClathrate 196.8 Si₁₈N₂₄ Type I Clathrate  96.08 Si₂₃N₂₃ Type I Clathrate114.13 C₆Si₄₀ Type I Clathrate  62.9 C (Diamond) Diamond cubic 438.8442* α-C₃N₄ Hexagonal 378.7 β-C₃N₄ Cubic spinel 419.1 c-Si₃N₄ Cubicspinel 300 300* SiC Cubic (Zinc blend) 225*

Also shown in Table 1 for comparison are theoretical or experimentaldata (indicated by an asterisk) of bulk modulus for diamond, carbonnitride, silicon nitride, and silicon carbide from the literature. Theresults in Table 1 indicate that a wide range of bulk modulus can beobtained from Type I hybrid C—N, N—Si, and C—Si clathrates, depending onthe framework atoms. As can be seen, carbon clathrate compounds exhibitbulk moduli that are in the range of 245 GPa to 374 GPa. Examples ofclathrates herein (C₁₈N₂₄, C₂₃N₂₃, Li₈C₂₃N₂₃, Si₁₈N₂₄, Si₂₃N₂₃) areidentified, and it is therefore contemplated that the carbon-nitrogen,nitrogen-silicon and nitrogen-carbon-silicon clathrates herein willsimilarly indicate bulk modulus values in the range of 245 GPa to 374GPa, depending upon the final composition selected.

1. A composition comprising a Type I clathrate of silicon having a Si₄₆framework cage structure wherein the silicon atoms on said framework areat least partially substituted by nitrogen atoms, said compositionrepresented by the formula N_(y)Si_(46-y) with 1≦y≦45.
 2. Thecomposition of claim 1 wherein said composition is in the form of abattery electrode.
 3. The composition of claim 1 wherein said electrodecomprises an anode electrode in a Li battery.
 4. The composition ofclaim 1 wherein said electrode comprises a cathode electrode in a Libattery
 5. The composition of claim 1 further including one or moreguest atoms within said cage structure, represented by the formulaA_(x)N_(y)Si_(46-y) where, A=H, Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr,Ba, Ra, Eu, Cl, Br, I, and any metal or metalloid element, with 1≦y≦45and x is the number of guest atoms within said cage structure.
 6. Thecomposition of claim 5 wherein x is greater than zero and less than orequal to
 200. 7. The composition of claim 5 wherein A is Li.
 8. Thecomposition of claim 5 wherein x has a value such that the cagestructure undergoes a volume expansion of less than or equal to 50.0%.9. A composition comprising a Type I clathrate of silicon having a Si₄₆framework cage structure wherein the silicon atoms on said framework areat least partially substituted by nitrogen and carbon, said compositionrepresented by the formula N_(y)C_(z)Si_(46-y-z) with 1≦y≦44 and1≦z≦45−y.
 10. The composition of claim 9 wherein said composition is inthe form of a battery electrode.
 11. The composition of claim 9 whereinsaid electrode comprises an anode electrode in a Li battery.
 12. Thecomposition of claim 9 wherein said electrode comprises a cathodeelectrode in a Li battery.
 13. The composition of claim 9 furtherincluding one or more guest atoms within said cage structure,represented by the formula A_(x)N_(y)C_(z)Si_(46-y-z) where, A=H, Li,Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Eu, Cl, Br, I, and any metalor metalloid element, with 1≦y≦45 and 1≦z≦45−y and x is the number ofguest atoms within said cage structure.
 14. The composition of claim 13wherein x is greater than zero and less than or equal to
 200. 15. Thecomposition of claim 13 wherein A is Li.
 16. The composition of claim 13wherein x has a value such that the cage structure undergoes a volumeexpansion of less than or equal to 50.0%.